Efficient gas exchange by the mammalian lung is dependent upon several factors, including the volume and viscosity of the aqueous fluid bathing the lung epithelia. These physical characteristics of the aqueous fluid are dependent upon proper function of alveolar epithelial cells, particularly type II alveolar cells. Type II cells are responsible for secretion of surfactant (a mixture of phospholipids, principally lecithin and sphingomyelin). The surfactant reduces the surface tension of the aqueous fluid bathing the alveoli and contributes to the elastic properties of pulmonary tissue.
Cystic fibrosis is an example of a pulmonary disease associated with the accumulation of thick mucosal secretions which impair alveolar ventilation and O.sub.2 /CO.sub.2 exchange. Cystic fibrosis is an autosomal recessive genetic disorder characterized by defective fluid secretion in epithelia of the pancreas, small intestine, sweat glands, and airways. The gene to which the defect in cystic fibrosis is attributed encodes a protein which has been characterized as a transmembrane conductance regulator (Riordan et al., Science 245:1066-1072, 1989; Kerem et al., Science 245:1073-1080, 1989). This protein appears to play a role in the functioning of an airway epithelial cell anion channel (Liedtke, FASEB 6:3076-3084, 1992). This anion channel, generally identified as a Cl.sup.- channel, may also act as a channel for secretion of other ions (Smith and Welsh, J. Clin. Invest. 89:1148-1153, 1992; Kunzelmann et al. Pflugers Arch. 417:616-621, 1991).
The pulmonary symptoms of cystic fibrosis and other diseases involving accumulation of thick mucous secretions in the lungs are typically treated with respiratory modalities intended to mobilize the secretions, including regular percussion and postural draining. Various therapeutic aerosols designed to liquefy the mucus or enzymatically digest proteins, nucleic acids, or other mucus components are known in the art (U.S. Pat. No. 2,905,589; U.S. Pat. No. 5,279,823; WO 93/03709; Lourenco and Cotromanes, Arch. Intern. Med. 142:2299-2308, 1982).